Production of large-surface-area mouldings generally requires a low coefficient of thermal expansion, and also good dimensional stability and geometric stability, and high stiffness. These properties can be achieved by adding fillers or reinforcing materials. High tensile moduli of elasticity can in particular be realized by adding fibrous reinforcing materials with high aspect ratio, i.e. with a large fibre length/fibre diameter quotient. Materials particularly attractive in technical terms for this purpose are glass fibres or carbon fibres, and from a commercial point of view particular preference is given to glass fibres; chopped fibres are particularly easy to handle in the production of the compounded materials and are therefore particularly preferred because they can be used in commercially available compounding assemblies such as single- and twin-screw extruders, preferably with side-feed of the glass fibres directly into the previously melted and dispersed polymer composition. However, addition of the fillers, and in particular addition of glass fibres and carbon fibres, has a severe adverse effect on the toughness of the moulding compositions. These circumstances place practical limitations on the reinforcing materials that can be used and the fill levels that can be realized, and therefore the stiffness values that can be achieved for the material. These filler-reinforced polymer compositions of the prior art therefore often have inadequate scope for application. In particular, these reinforced polymer compositions disclosed in the prior art cannot realize very thin-walled large-surface-area mouldings or applications with relatively high component-ductility requirements, for example structural or safety components for the automobile sector, or can do so only by incurring relatively high engineering costs. For these application sectors there is therefore a requirement for provision of polymer compositions with good processability in the injection-moulding process (high melt flowability) and with a combination of high tensile modulus of elasticity and improved ductility not only on exposure to unidirectional impact but also in particular on exposure to multiaxial load, for example in the drop test. Because use of innovative processing technologies, for example variotherm injection moulding, can now produce excellent surface appearance (class A surface) even when reinforced polymer materials are used, there is also an increasing trend towards use of uncoated components produced from such compositions, in order to save costs. A preferred embodiment of this trend requires the provision of reinforced polymer compositions which have good processability and a combination of high modulus of elasticity and improved ductility and which moreover exhibit good resistance to ageing effects caused by, for example, light and heat, and preferably also to contact with chemicals (stress-cracking resistance), without any need for further surface finishing (coating).
Glass-fibre-reinforced polycarbonate compositions comprising rubber-modified vinyl copolymers are in principle already known from the prior art. However, the polycarbonate compositions of the prior art do not exhibit the combination of all of the desired property features previously described. In particular, the ductility of the material is generally unsatisfactory in these polycarbonate compositions where the quantity of glass fibres used is suitable to achieve stiffness values that are adequate for thin-walled applications.
EP 0 624 621 A2 discloses polycarbonate compositions with improved toughness and ductility comprising from 10 to 80% by weight of polycarbonate, from 10 to 80% by weight of rubber-modified graft copolymer and from 5 to 50% by weight of glass fibres, with a coating comprising polyolefin wax.
WO 84/04317 A1 discloses polycarbonate compositions with high impact resistance and high modulus comprising polycarbonate, styrene resin, optionally up to 10 parts by weight, based on the entirety of polycarbonate, styrene resin, glass fibre and silicone, of impact modifier, glass fibres and a polyhydrogensiloxane, an essential criterion of the invention here being use of unsized glass fibres.
EP 1 802 696 A1 discloses long-glass-fibre-reinforced polymer compositions with an improved combination of mechanical properties, in particular tensile strength, tensile modulus of elasticity and impact resistance, comprising at least one polymer selected from the group of the polyamides, polycarbonates, polyester carbonates, graft polymers and copolymers, and also comprising a terpolymer of styrene, acrylonitrile and maleic anhydride and long glass fibres.
WO 2009/021648 A1 and the associated DE 10 2007 038438 A1 disclose glass-fibre-reinforced polycarbonate compositions with high stiffness, impact resistance, flowability, processing stability, and chemical resistance, and good ageing resistance to effects caused by light and by heat, comprising from 10 to 85 parts by weight of polycarbonate, from 10 to 50 parts by weight of rubber-free vinyl copolymer, from 5 to 50 parts by weight of epoxy-sized glass fibres, from 0 to 2 parts by weight of rubber-modified graft polymer and from 0 to 10 parts by weight of polymer additives. The glass fibre C-1 used according to the invention in this prior art is also termed component C-1 in the experimental section of the present application, and is used in comparative examples.
However, the melt-flowability, ageing resistance, stiffness and/or ductility of the glass-fibre-reinforced polycarbonate compositions disclosed in the prior art is inadequate for critical applications.